While this installation procedure is sufficient for most extensions, some require a different installation procedure. Check your extension's documentation for details.

If you want to alter configuration variables in LocalSettings.php, you have to do this typically after including the extension. Otherwise defaults defined in the extension will overwrite your settings.

Atención:

While extension declaration can be placed in other places within the LocalSettings.php file, never place extensions before the require_once "includes/DefaultSettings.php"; line for MediaWiki versions below 1.17 . Doing so will blank the extension setup function arrays, causing no extensions to be installed, and probably will make your wiki inaccessible until you fix it!

Upgrading an extension

Some extensions require to be updated whenever you update MediaWiki, while others work with multiple versions.
To upgrade to a new version of an extension:

Download the new version of the extension

Replace all the extension files in the extension/ExtensionName directory with the new files. Do not remove the extension configuration present in LocalSettings.php

Depending on the extension, you may have to run the Update.php maintenance script. Most extensions will mention if this script needs to be run or not. (Running the update.php script when its unnecessary will not hurt anything, so if you're unsure don't be afraid to run it). If you don't have command line access, you can also use the web updater.

That's all you need to do. In most cases any extension configuration you have in LocalSettings.php will also work with the newer version of the extension.

These instructions cover 99% of extensions. If the specific extension you are upgrading has instructions that differ from these, you should probably follow the specific extension's instructions

Uninstalling an extension

Extensions are added by adding a line to LocalSettings.php, which basically looks like this:

Depending on the extension you want to uninstall additionally other stuff might be done on installation, which you want to undo now. For details see the section on installing an extension.

Remove this line and the extension is uninstalled. If you want to, you can (and if you do not want to use this extension in the future you should) remove the files of this extension inside the folder "extensions/".

Maybe you also have some other lines in LocalSettings.php, which have to do with the extension you want to remove. Most likely this will be lines, which give certain users the right to access pages, which are provided by the extension. These lines contain the variable "$wgGroupPermissions" and make some settings there. As far as they have to do with rights, which come from the removed extension, you can remove these lines as well.

Maybe your extension also has added columns to your database. The updater maintenance/update.php removes them, when you run it, after you have uninstalled the extension.